Silicon carbide (SiC) bipolar junction transistors (BJTs) and other bipolar devices are high-performance power devices having low on-state and switching losses and are also capable of high-temperature operation due, in part, to the high breakdown electric field, high thermal conductivity and high saturated drift velocity of electrons in SiC. SiC is a wide bandgap semiconductor and, therefore, may advantageously be used for manufacturing devices (such as bipolar devices) for high power, high temperature and high frequency applications.
High-power bipolar junction transistors (BJTs) (including a collector region, a base region and an emitter region) can be used as standalone devices in high-power applications, or can be incorporated in other high-power bipolar semiconductor devices, such as insulated-gate bipolar transistors, thyristors, and so forth. One of the critical characteristics representative of the performance of a high-power BJT (a BJT power device) are common emitter current gain (which may be referred to as ECG or beta). A BJT with a low ECG may consume too high a drive current. An IGBT with a low ECG of the built-in bipolar transistor may have too high of a forward voltage drop. The same concerns also apply for thyristor devices.
When designing high-power BJTs (and devices including the elements of a BJT, such as IGBTs and thyristors), making tradeoffs between performance parameters is typically required. For instance, improvements in ECG (beta) can be achieved by reducing acceptor dose (dopant dose) in the base region of a NPN BJT transistor. However, reducing the acceptor dose in the base region also reduces the blocking (breakdown) voltage of the BJT. Therefore, improvements in ECG can also result in a degraded blocking voltage for a given BJT. Similar design tradeoffs exist for other bipolar power devices, such as those that include the elements of a BJT (e.g., IGBTs and thyristors).
In BJTs, or other bipolar devices, a high value of ECG can be achieved with easy means by decreasing the total acceptor charge in the base. However, in a high power BJT such technique will come at the cost of a high drop in breakdown voltage from the theoretical due to early punch-through of the base region.